package com.fresh.utils;

import java.security.SecureRandom;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.SecretKeyFactory;
import java.math.BigInteger;
import java.security.NoSuchAlgorithmException;
import java.security.spec.InvalidKeySpecException;

/**
 * PBKDF2 salted password hashing. Author: havoc AT defuse.ca www: http://crackstation.net/hashing-security.htm
 */
public class PasswordHashUtil {

	public static void main(String[] args) throws NoSuchAlgorithmException, InvalidKeySpecException {
		System.out.println(PasswordHashUtil.createHash("123456"));
	}
	
	public static final String PBKDF2_ALGORITHM = "PBKDF2WithHmacSHA1";

	public static final int SALT_BYTES = 24;
	public static final int HASH_BYTES = 24;
	public static final int PBKDF2_ITERATIONS = 1000;

	public static final int ITERATION_INDEX = 0;
	public static final int SALT_INDEX = 1;
	public static final int PBKDF2_INDEX = 2;

	public static String createHash(String password) throws NoSuchAlgorithmException, InvalidKeySpecException {
		return createHash(password.toCharArray());
	}

	public static String createHash(char[] password) throws NoSuchAlgorithmException, InvalidKeySpecException {
		if (password.length == 0) {
			return null;
		}
		SecureRandom random = new SecureRandom();
		byte[] salt = new byte[SALT_BYTES];
		random.nextBytes(salt);
		byte[] hash = pbkdf2(password, salt, PBKDF2_ITERATIONS, HASH_BYTES);
		return PBKDF2_ITERATIONS + ":" + toHex(salt) + ":" + toHex(hash);
	}

	public static boolean validatePassword(String password, String goodHash) throws NoSuchAlgorithmException, InvalidKeySpecException {
		return validatePassword(password.toCharArray(), goodHash);
	}

	public static boolean validatePassword(char[] password, String goodHash) throws NoSuchAlgorithmException, InvalidKeySpecException {
		if (goodHash.contains(":")) {
			String[] params = goodHash.split(":");
			int iterations = Integer.parseInt(params[ITERATION_INDEX]);
			byte[] salt = fromHex(params[SALT_INDEX]);
			byte[] hash = fromHex(params[PBKDF2_INDEX]);
			byte[] testHash = pbkdf2(password, salt, iterations, hash.length);
			return slowEquals(hash, testHash);
		} else {
			return false;
		}
	}

	private static boolean slowEquals(byte[] a, byte[] b) {
		int diff = a.length ^ b.length;
		for (int i = 0; i < a.length && i < b.length; i++) {
			diff |= a[i] ^ b[i];
		}
		return diff == 0;
	}

	private static byte[] pbkdf2(char[] password, byte[] salt, int iterations, int bytes) throws NoSuchAlgorithmException, InvalidKeySpecException {
		PBEKeySpec spec = new PBEKeySpec(password, salt, iterations, bytes * 8);
		SecretKeyFactory skf = SecretKeyFactory.getInstance(PBKDF2_ALGORITHM);
		return skf.generateSecret(spec).getEncoded();
	}

	private static byte[] fromHex(String hex) {
		byte[] binary = new byte[hex.length() / 2];
		for (int i = 0; i < binary.length; i++) {
			binary[i] = (byte) Integer.parseInt(hex.substring(2 * i, 2 * i + 2), 16);
		}
		return binary;
	}

	private static String toHex(byte[] array) {
		BigInteger bi = new BigInteger(1, array);
		String hex = bi.toString(16);
		int paddingLength = (array.length * 2) - hex.length();
		if (paddingLength > 0) {
			return String.format("%0" + paddingLength + "d", 0) + hex;
		} else {
			return hex;
		}
	}
}
